Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $86.47   8.153%   $93.5199   $93.52   $93.50   $93.50  
  Purchase #2 $160.56   3.814%   $166.6838   $166.68   $166.70   $166.70  
  Purchase #3 $132.77   8.523%   $144.086   $144.09   $144.10   $144.10  
  Purchase #4 $42.79   13.552%   $48.5889   $48.59   $48.60   $48.60  
  Purchase #5 $247.43   10.256%   $272.8064   $272.81   $272.80   $272.80  
  Purchase #6 $66.59   3.829%   $69.1397   $69.14   $69.15   $69.10  
  Purchase #7 $233.77   12.332%   $262.5985   $262.60   $262.60   $262.60  
  7 purchase totals = $970.38       $1,057.4232   $1,057.43   $1,057.45   $1,057.40